1. Field of the Invention
The invention relates to the production of hydrogen from ammonia. The produced hydrogen is used as fuel in a fuel cell.
2. Description of Related Art
An article by G. Strickland entitled “Hydrogen Derived from Ammonia: Small-Scale Costs”, Int. J. Hydrogen Energy, Vol. 9, No. 9, pp 759-766 (1984) states that hydrogen derived from anhydrous liquid NH3, via a dissociator and H2 purifier, offers an alternative to conventional methods of obtaining pure H2 for small-scale use. The specific process outlined in the article employees a poly-bed pressure swing adsorption (PSA) system for the H2 purification step. It is stated that when using this purification step in conjunction with ammonia dissociation, about 75% of the hydrogen could be recovered with a fuel credit obtained for the remainder.
European patent application No. 83306428.0 discloses a method and apparatus for the production and delivery of hydrogen, especially adapted for on-site production for hydrogen users requiring on the order of 28 to 2800 m3 of hydrogen per day. According to the disclosure, hydrogen is produced by first dissociating ammonia in a typical dissociation reactor, and subsequently passing the ammonia feed stream to a bed of hydridable material which exothermically and selectively adsorbs hydrogen from the feed stream and endothermically desorbs hydrogen on demand. The H2 purification hydride system comprises at least one flow through reactor having inner and outer heat exchange shells and a bed of hydridable material located co-axially there between. Additionally, a means for circulating fluid through the heat exchanger shells whereby heat may be extracted therefrom during adsorption of hydrogen from the feed and whereby heat may be supplied thereto when hydrogen is desorbed from the hydride bed. It is stated that the heat transfer characteristics of the flow-through reactor of the disclosed invention are at the heart of its performance. The heat flow is interrelated to flow rate, pressure and recovery and those variables operate to establish the effective hydrogen adsorption pressure.
Sheridan, et al. (U.S. Pat. No. 4,360,505) discloses an improved adiabatic process for separating hydrogen from mixed gas streams using hydridable materials as the adsorbing medium. The improvement involves utilizing a composite comprising a thermal ballast in admixture with the hydride material to adsorb the heat of the reaction and to aid in desorption. By virtue of the intimate contact of the ballast with the hydridable material, rapid cycle times plus good bed utilization are achieved.
Despite these advancements in the art, a need exists for an improved, efficient means of producing fuel for a fuel cell from an ammonia source.